EGR

Exhaust Gas Recirculation routes part of the exhaust back into the engine’s scavenge air to lower peak combustion temperature and suppress thermal NOx formation, an in-engine route to MARPOL Annex VI Tier III without a separate reactor. It avoids the urea supply chain that SCR needs but adds a scrubber and water-treatment loop to clean the recirculated gas, and it slightly raises fuel consumption. Two-stroke makers offer it as the Tier III alternative to SCR, with the choice turning on fuel type, space, and operating profile inside NOx-ECAs.